The present invention relates to an automobile which needs a plurality of different voltages, in order to correspond to the increase in the consumption of the electric power in an automobile, and the power-supply unit therefor. Especially, the present invention relates to a technology suitable to achieve a plurality of voltage power supply at low-cost.
To realize an electric operation and a large capacity of on-board equipment such as electric power steerings and electric air conditioners provided in automobiles, 42V automobile electric power supply system in which the 42V-system power supply is added to the conventional 14V-system power supply is proposed. The electric current decreases to ⅓ of the conventional current amount because the voltage increases to three times that of the conventional power supply in the 42V-system power supply. Therefore, the decrease in the power loss, the weight saving of the harness, and the adoption of the high-power load, etc. become possible.
However, because making the electric power load like a lamp system, etc. a 42V-system is difficult, it is expected that two kinds of voltages of 14V and 42V are used for the present time.
The system having both of the battery (rated voltage 36V) for 42V and the battery (rated voltage 12V) for 14V is proposed, in which the battery for 42V is charged by an alternator and the battery for 14V through a DC/DC converter.
Another method is proposed to reduce the cost, in which the switch switches the output of the alternator to the 42V side or the 14V side, and the DC/DC converter is omitted.
A further method is proposed, in which two batteries are connected in series, two kinds of voltage terminals are provided, and the charge to each battery is switched by switching the switching element. If this method is applied to 42V power supply, the battery for 14V need not be separately prepared because the battery gives the terminal for 14V for 42V. An example of this method is described in the U.S. Pat. No. 4,686,442.
A further method is proposed to increase the efficiency of the alternator and the lifetime of the starter, in which the function of the starter and the alternator is integrated and the motor/generator controlled by the inverter is applied to the 42V-power supply.
There is a problem that the battery cannot be charged at all when the controller for controlling the switch breaks down, and the switch cannot be turned on, in the method in which the output of the alternator is switched to 42V side or 14V side with switch among the above-mentioned methods. Moreover, it is necessary to provide the battery for 14V besides the battery for 42V, and thus the cost rises.
In the method that two batteries are connected in series, two kinds of voltage terminals are provided, and the charge to each battery is switched by switching the switching element, only the direction of the charge from the alternator is considered in the configuration of the switching element. Therefore, there is a problem that it is not possible to apply the method to the motor/generator in which the function of the starter is integrated, because the electric current cannot flow into the direction of the electric discharge.
In either example, the change in the power-supply voltage occurred when the switch is changed is not considered.
An object of the present invention is to provide an automobile and the power-supply unit therefor operable even if the DC/DC converter is not used, a plurality of batteries are not needed, and the controller for controlling the switch breaks down.
Another object of the present invention is to provide an automobile and the power-supply unit therefor which can control so that the change in the power-supply voltage may decrease when switching on/off.
A power-supply unit of the automobile according to the present invention includes a battery having a high-voltage terminal and a low-voltage terminal, a converter for converting AC power into DC power, a first switching element for controlling the power supply in one direction from the high-voltage terminal of the battery to the converter, and a second switching element for controlling the power supply in one direction from the converter to the low-voltage terminal of the battery.
It becomes possible to achieve a power supply system with a plurality of voltages without using a DC/DC converter by this configuration.
Further, because a plurality of voltage terminals are provided in one battery, it is not necessary to provide a battery separated for each voltage.
Preferably, the first and the second switching element of the present invention comprise a field effect transistor and diodes connected mutually and oppositely.
Preferably, the voltage at the DC side of the converter is controlled to the voltage of the high-voltage terminal side or that of the low-voltage terminal side according to the on/off state of the switching element.
Preferably, even when it becomes impossible to control the first and the second switching element due to the breakdown of the controller, the voltage of the DC side of the converter is controlled according to the direction of the electric power converted by the converter.
Even when it becomes impossible to control the switching elements hereby, the charge to the high-voltage terminal side and the electrical discharge from the low-voltage terminal side are always possible due to the operation of the diode connected mutually and oppositely. Therefore, the automobile can be operated until the remaining amount of the low-voltage terminal side of the battery is run out.
Preferably, the present invention further comprises the charging rate measuring means for measuring the charging rate at the high-voltage terminal side of the battery and that at the low-voltage terminal side, respectively. The first and the second switching element are controlled. according to the measured charging rate.
As a result, it is possible to control so as not to cause the unbalance in the battery charging rate at the high-voltage terminal side and the low-voltage terminal side, and the deterioration of the battery performance due to the unbalance of the charging rate can be prevented.
Preferably, in the present invention, when the DC voltage is controlled by the converter, the voltage of another voltage terminal not controlled is detected directly, and the voltage control system is corrected.
As a result, it becomes possible to control so that the terminal voltage does not greatly change even when the switching element is switched.
An automobile of the present invention has a motor/generator; an inverter for driving said motor/generator; a battery connected to said inverter through the terminals at a plurality of different voltages; a first switching element provided between said inverter and a first fixed terminal of the terminals at a plurality of different voltages of said battery; a first rectifying device connected in parallel with the intermittence-switching means provided in said first switching element, for throwing more electric currents in the direction of said first terminal from said inverter; a second switching element provided between said inverter and a second terminal at a voltage lower than that of said the first terminal of the terminals of a plurality of different voltages of said battery; a second rectifying device connected in parallel with the intermittence-switching means provided in said second switching element, for throwing more electric currents in the direction of said second terminal from said inverter; and a battery control unit for turning on/off said first and said second switching element according to the state of the charge of said battery.
Further, in the automobile of the present invention, said first switching element and said first rectifier, and said second switching element and said second rectifier are a first and a second field effect transistor, respectively.